The most common and most likely answer to this crossword clue is the 8 letter word BREECHES
I've seen this crossword clue in Financial Times
B
R
E
E
C
H
E
S
Buddy explains!

The straight part
We know that "Pants" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pants = breeches.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BREECHES mean?
BREECHES noun- (now only in the plural) A garment whose purpose is to cover or clothe the buttocks.
- The buttocks or backside.
- The part of a cannon or other firearm behind the chamber.
- The external angle of knee timber, the inside of which is called the throat.
- A breech birth.
- A garment worn by men, covering the hips and thighs; smallclothes.
- Trousers; pantaloons.